Transformers transfer electrical energy from one circuit to another via inductively coupled conductor coils. More specifically, a varying current in a primary coil winding creates a varying magnetic flux in a core of the transformer, which in turn generates a varying magnetic field (i.e. induced voltage) through a secondary coil winding. When a load is connected to the secondary winding, an electric current will flow in the secondary winding thereby transferring electrical energy through the transformer to the load. The induced voltage in the secondary winding is proportional to the primary voltage and is determined by the ratio of the number of turns in the secondary winding to the number of turns in the primary winding. A transformer may therefore be configured to “step up” an ac voltage by making the number of turns in the secondary winding greater than the number of turns in the primary winding, or “step down” an ac voltage by making the number of turns in the secondary winding less than the number of turns in the primary winding.
Particular embodiments of the invention relate to transformers suitable for use in power conditioning units for delivering power from a dc power source (e.g. a photovoltaic module) to an ac output. Such power conditioning units are described in the Applicant's earlier published patent applications, for example, WO2007/080429. In that case, the power conditioning unit comprises an input for receiving power from a dc power source, an output for delivering ac power, an energy storage capacitor, a dc-to-dc converter having an input connection coupled to the input and an output connection coupled to the energy storage capacitor, and a dc-to-ac converter having an input connection coupled to the energy storage capacitor and an output connection coupled to the output and wherein a transformer is provided in the dc-to-dc converter.
It is an aim of the present invention to provide a transformer construction with minimal size and optimum efficiency and which may be suitable for use in power conditioning units such as those described above.